Method for manufacturing safety vent on cover of lithium-ion battery

ABSTRACT

A method for manufacturing a safety vent on a cover of a lithium-ion battery has punching the cover to form an annular recess and the cover made of aluminum alloy; heating the annular recess to a temperature between 200° C.˜500° C.; cooling the annular recess; and obtaining the safety vent on the cover of the lithium-ion battery. The aluminum alloy can be heated to a specific temperature for lowering its stress, so a thickness between a lower surface of the cover and a bottom of the annular recess is neither necessary to be precisely controlled, so retaining yield of lithium-ion batter

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a method for manufacturing a safety vent, and more particularly to a method for manufacturing a safety vent formed on a cover of a lithium-ion battery, which improves yield of the lithium-ion battery.

2. Description of the Related Art

A lithium-ion battery has a lot of advantages including large capacity, high energy-density, high power density, stable discharge, long shelf life, no memory effect and so on. Thus, the lithium-ion battery has broad applications. Especially in electronics industry, the lithium-ion battery is used to power small electronic products, such as mobile phones, personal digital assistants (PDA), portable computers and the like.

However, pressure in a shell of the lithium-ion battery will be increased due to rapid evaporation of electrolyte or other side effect causing a large amount of gas and heat during abnormal charge and discharge. Once the pressure exceeds critical value, the lithium-ion battery will explode or be on fire. Therefore, a safety vent is required in a cover of the shell of the lithium-ion battery. When a large amount of gas in the shell generates in the shell, the gas is able to burst the safety vent, so the pressure in the shell is released.

With reference to FIG. 4, a conventional method for manufacturing safety vent (22) on a cover (21) of a lithium-ion battery comprises directly punching the cover (21) of the lithium-ion battery to form an annular recess (221). Nevertheless, a thickness between a bottom (222) of the annular recess (221) and a lower surface (211) of the cover (21) has to be precisely controlled to between 0.02 mm to 0.03 mm, so the safety vent (22) can be broken through when pressure in a shell of the lithium-ion battery is 15˜25 kg/cm².

If the thickness between the bottom (222) and the lower surface (211) is too thick, the safety vent (22) cannot be burst through, which damages the lithium-ion battery. But if the cover (21) is punched too deeply and the thickness between the bottom (222) and the lower surface (211) is too thin, the cover (21) may be damaged to lower the yield of lithium-ion battery or the safety vent (22) may easily burst through during normal use.

To overcome the shortcomings, the present invention provides a method for manufacturing a safety vent to mitigate or obviate the aforementioned.

SUMMARY OF THE INVENTION

The primary objective of the present invention is to provide a method for manufacturing a safety vent formed on a cover of a lithium-ion battery, which improves yield of the lithium-ion battery.

To achieve the objective, the method for manufacturing the safety vent on the cover of the lithium-ion battery in accordance with the present invention comprises punching the cover to form an annular recess and the cover made of aluminum alloy; heating the annular recess to a temperature between 200° C. 500° C.; cooling the annular recess; and obtaining the safety vent on the cover of the lithium-ion battery.

The aluminum alloy can be heated to a specific temperature for lowering its stress, so a thickness between a lower surface of the cover and a bottom of the annular recess does not need to be precisely controlled, so retaining yield of lithium-ion battery.

Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a method for manufacturing a safety vent on a cover of a lithium-ion battery in accordance with the present invention;

FIG. 2 is a perspective view of a cover with a safety vent of a lithium-ion battery in accordance with the present invention;

FIG. 3 is a cross sectional side view of the cover with the safety vent of the lithium-ion battery in FIG. 2; and

FIG. 4 is a cross sectional side view of a cover with a conventional safety vent of a conventional lithium-ion battery in accordance with the prior art.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1 to 3, a method for manufacturing a safety vent on a cover of a lithium-ion battery in accordance with the present invention comprises punching the cover (11) to form an annular recess (121) (a); annealing the annular recess (121) (b); and obtaining the safety vent (12) on the cover (11) of the lithium-ion battery (c).

In the step of punching the cover (11) to form an annular recess (121) (a), the cover (11) has a lower surface (111) and is made of aluminum alloy and the annular recess (121) has a bottom (122). A thickness between the lower surface (111) of the cover (11) and the bottom (122) of the annular recess (121) is between 0.05 mm and 0.07 mm.

The step of annealing the annular recess (121) (b) comprises heating the annular recess (121) (b-1) to a temperature between 200° C.˜500° C. and cooling the annular recess (121). Preferably, the annular recess (121) is heated to a temperature of 400° C. Preferably, the annular recess (121) is cooled naturally.

With reference to FIGS. 2 and 3, a lithium-ion battery has a shell (10). The shell (10) is made of aluminum alloy and has a body and at least one cover (11). Each cover (11) may be formed with at an end of the body of the shell (10) integrally or may be formed prior to connecting to the body of the shell (10). The cover (11) has a lower surface (111) and a safety vent (12). The safety vent (12) is manufactured by the method of the present invention and comprises an annular recess (121). The annular recess (121) has a bottom (122) that has been annealed. The cover (11) further has a thickness between the lower surface (111) of the cover (11) and the bottom (122) of the safety vent (12). The safety vent (12) bursts through under a pressure from 18˜22 kg/cm m² when the thickness is from 0.05 mm to 0.07 mm.

The aluminum alloy can be heated to a specific temperature for lowering its stress, so even though the thickness between the lower surface (111) of the cover (11) and the bottom (122) of the safety vent (12) of the present invention is double the thickness of the prior art, the safety vent (12) still can be burst through under the pressure between 18˜22 kg/cm². Therefore, the thickness is neither necessary to be precisely controlled nor required as thin as that of the prior art, so retaining yield of lithium-ion battery. Furthermore, the range of pressure to burst through the safety vent (12) of the present invention is more concentrated than the range of pressure to burst through that of the prior art.

Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. A method for manufacturing a safety vent on a cover of a lithium-ion battery comprising: punching the cover to form an annular recess and the cover made of aluminum alloy; heating the annular recess to a temperature between 200° C.˜500° C.; cooling the annular recess; and obtaining the safety vent on the cover of the lithium-ion battery.
 2. The method as claimed in claim 1, wherein in the step of punching the cover to form an annular recess, a thickness between a lower surface of the cover and a bottom of the annular recess is between 0.05 mm and 0.07 mm.
 3. The method as claimed in claim 1, wherein in the step of heating the annular recess, the annular recess is heated to a temperature of 400° C.
 4. The method as claimed in claim 2, wherein in the step of heating the annular recess, the annular recess is heated to a temperature of 400° C.
 5. The method as claimed in claim 1, wherein the steps of heating the annular recess and cooling the annular recess forms a step of annealing the annular recess, which is performed after the step of punching the cover.
 6. The method as claimed in claim 2, wherein a step of annealing the annular recess having the steps of heating the annular recess and cooling the annular recess are performed after the step of punching the cover.
 7. The method as claimed in claim 3, wherein a step of annealing the annular recess having the steps of heating the annular recess and cooling the annular recess are performed after the step of punching the cover.
 8. The method as claimed in claim 4, wherein a step of annealing the annular recess having the steps of heating the annular recess and cooling the annular recess are performed after the step of punching the cover. 